Chromium metallurgy



Oct. 17, 1,939.

M. J. UDY

CHROMIUM METALLURGY Filed Sept. 7, 1958 ramz'le, calca/m i Imm/@auleeagen I urnace Crucible; INVENTOR MdL/@Cile (o man MARvxN J. UDY:imma/m,- earm BY WVM-ian ATTORNEYS Patented Oct. 17, 1939.

UNITED STATES PATENT oFFicE 45 Claims.

This invention relates to chromium metallurgy and has for an object theprovision of certain improvements relating to chromium-bearing productsand methods of producing such products. More particularly, the inventioncontemplates the production of improved chromiumbearing materials andimproved composite reagents for use in producing ferrochromium and foruse in incorporating chromium in iron and steel, the provision ofimproved methods of producing chromium-bearing materials and improvedcomposite reagents for such uses and the provision of improved methodsof producing ferrochromium and chromium-bearing iron and steellproducts. A further object of the invention is to provide certainimprovements in methods of utilizing high-carbon ferrochromium in theproduction of low-carbon ferrochromium and chromium-bearing iron andsteel products. The invention further contemplates the provision ofcomposite reagents of various compositions suitable for effective andefficient use in operations characterized as to type by performance inelectric furnaces, combustion furnaces, foundry ladies, crucibles andother types of equipment.

As hereinafter employed and as employed in the claims, the termferrochromiurn, as used to define metallic productsl subjected tooxidation treatments, unless qualified, includes all products containingiron and chromium and which also contain carbon in undesirable amountsrelatively to the chromium contents, Which amounts-can be reducedeffectively by means of the oxidizing treatments to provideproducts moresuitable than the original material for use in forming metallic productscontaining chromium; and the meaning of the term roasting, unlessqualified, is re`-` stricted to cover oxidizing operations in which thematerials undergoing treatment are subjected, in the solid state, to theaction of oxidizing gases, such as air, at elevated temperatures.

The invention deals with the difficult problem of carbon elimination andsuppression faced by chromium metallurgists, and it provides aneffective and efficient solution for that problem.

In the production of alloys containing chromium and iron, control ofcarbon is an important factor. Many of the more important alloys mustcontain carbon in amounts notexceeding very low percentages. Chromiumfor use in producing (Cl. 'l5-27) such alloys is obtained initially byreduction of natural chromium-bearing ores which also contain iron. Suchores commonly are reduced by carbon, for economic reasons, and.'becauseo! the great amnity of chromium for carbon, and because iron isreduclble at chromium reduction temperatures, the reduction products aremetals in the form of alloys or mixtures of iron and chromium(ferrochromium) contaminated with considerable amounts of carbon. The 1amounts of carbon contained in ferrochromium products resulting fromcarbon reduction make all of such products unsuitable for direct use inthe productionof many alloys containing iron and chromium andelimination of the carbonl therefore is necessary in many instances.

For the same reason that it is diillcult or imv possible to excludecarbon from ferrochromium in reduction with carbon, complete eliminationof carbon from carbon-bearing ferrochromium after 0 production has beendimcult or impossible.

Many procedures have been proposed for reducing the carbon inferrochromium, and for utilizing reducing agents other than carbon toavoid its incorporation in the ferrochromium in 25 the first instance,in order to produce ferrochromium products suitable for direct use inproducing low-carbon alloys containing iron and chromium. Many of theprocedures proposed heretofore can be operated successfully technically,.but are economically unsound.

In industrial operations, for the most part, ferrochromium of the verylow carbon content required in the production of low-carbon alloyscontaining iron and chromium (for example, chromium steels containing.06 per cent to .20 per cent C) has been secured by replacement of thecarbon in high-carbon ferrochromium with silicon followed by removal ofthe silicon by oxidation, as by treatment with more chromium-bear- 40ing ore. The present invention provides another, more effective and moredenitely controllable method of removing carbon from high-carbonferrochromium. The method of the invention accomplishes carbon removalby oxidation of the metal and carbon of the ferrochromium to produce a.concentrated oxidized chromium product from which the chromium can bereduced again readily by means of silicon, or a similar noncarbonaceousreducing agent. According to this l0 invention an agent like silicon-isutilized indirectly for aiding in obtaining low-carbon chromiumproductsfrom chromite ores; The controlled oxidation of silicon in accordancewith the invention distinguishes the method of the invention from theprior art method and makes the method of the invention more eiiectiveand more economical. 1

'Ihis invention is based on my discovery that products resulting fromcontrolled oxidation of ferro-chromium are particularly well adapted foruse in the production of exothermic mixtures capable of reacting withinthemselves to produce metallic chromium at temperatures normallyemployed in operations designed for the production of alloys o! chromiumand iron.

The improved products of my invention are produced by subjectingcarbon-bearing ferrochromium to controlled oxidizing treatments to formproducts containing oxides of iron and chromium, free or substantiallyfree of metal and containing carbon in an amount less than thatcontained in the ferrochromium employed. 'I'he ierrochromium may beoxidized either in the molten state or in the solid state, and theoxidation treatment may be controlled to eect any desired degree ofcarbon elimination. 'I'he degree of carbon elimination effected in anyoxidation treatment will depend upon the carbon specication o! thechromium-bearing product to be produced through the use ot theparticular material of the oxidation treatment.

The ferrochromium may be subjected to the oxidizing treatment alone orin the presence of one or more addition agents such as lime or soda ashwhich serve as oxidation promoters and which react with the oxidesresulting from oxidation of the iron and chromium. When the.ferrochromiurn is subjected to the oxidizing treatment alone in theilrst instance the product of such oxidizing treatment may be subjectedto a iurther oxidizing treatment in the presence of one or more agentsof the aforementioned type to accomplish further oxidation, to bind theoxides chemically, or to accomplish both of these objectives.

The composite reagents o! my invention comprise iron and chromiumoxide-bearing products resulting from the oxidation of ferrochromium andone or more solid, non-carbonaceous reducing agents such as aluminum orsilicon or an alloy of aluminum or silicon with one or more otherelements. The oxide-bearing material and the non-carbonaceous reducingagent are ilnely divided and intimately mixed. The degree of subdivisionand intimacy of mixing of components of the mixture preferably are suchthat every particle of reducing material contained in the mixture is indirect and substantially complete contact with particles of reducingagent. I have found that such intimate contact requires a degree o!comminution such that a large proportion of the oxide-bearing materialand the reducing agent consists of particles sumciently small to pass a100-mesh screen (Tyler series) and grinding of the materials in contact,or together.

The products o! oxidation treatments of terrochromium are admirablysuited for grinding to the degree ot tlneness necessary for the requiredintimate mixing and contact. Such products can be ground readily in anordinary ball mill substantially to impalpable powders.

The products o! oxidation, also, are admirably suited for use in formingexothermic mixtures,

and oxidation is readily controlled to form products containingsuillcient oxygen to support combustion of reducing agents which may besubstantially complete, if desired. The iron of the ferrochromium isconverted readily to ferrie oxide (Fez-Ox), and the chromium isconverted readily to chromic oxide (CrzOs) Oxidation may be iurthercontrolled to convert a large proportion of the chromium to chromicanhydride (CrOs) Depending upon the conditions under which the variouscomposite reagents are to be employed, they may contain additionaloxygen-containing substances to provide additional heat for melting themetal and slag produced.

Any of the common oxidizing agents such, for example, as sodium nitrate,sodium chlorate and manganese dioxide may be employed for promotingoxidation of silicon with the resultant production of additional heat.Such oxidizing agents are required, for example, when the reactionmixtures contain large amounts of inert materials such as slag-formingmaterials, and they are employed in amounts suillcient to produce enoughheat to melt the metal and slag produced and give the slag the desirediluidity. The addition of such oxidizing agents requires additionalsilicon, when silicon is employed for reduction, and the total amountsof silicon and available oxygen are so proportioned as to provide aboutthe theoretical amount of silicon for combining with the availableoxygen. I! excess silicon is used, the excess will enter the metalproduced, control of this being eil'ected in the use oi improvedoxidation products.

The products resulting from the roasting of ferrochromium in the solidstate to eilect a high degree ot elimination of carbon are particularlywell adapted for the production of a nely divided product by grinding.Therefore, the invention will be described more particularly hereinaiterwith reference to the production and use of such products.

Roasting in the solid state to eiIect a high degree of carbonelimination requires preliminary ilne grinding of the carbon-bearingferrochromium. I have i'ound products in which the major portion of theparticles are minus 100 mesh to be most suitable for effective removalof carbon by roasting. The roasting of the iinely divided particlesresults in the production oi' particles of the resulting oxidizedcompounds of the same general order of size as the particles otferrochromium treated. 'I'hese particles appear to consist ofagglomerates of even smaller particles formed as a result of oxidationof the individual atoms of the components of the ferrochromium. Roastingof the ilnely divided` ferrochromium tends to produce separatedparticles approaching the molecular sizes of the compounds formed, and,while the achievement of this objective is impossible, the character ofthe smaller particles produced, as indicated by the ease with which theparticles may be disrupted, indicates that the tendency is not arrestedentirely. The roastedi product as discharged or withdrawn from theroasting equipment will not necessarily be in the form of a powder as neas the ferrochromium powder employed in its production. Usually, it willcontain a large proportion of agglomerates of particles of the size ofand smaller than the particles of ferrochromium employed in itsproduction. 'Ihe particles comprising the agglomerates are relativelyloosely bound together and they may be separated readily by grinding.

Grinding of the roasted product breaks up the agglomerates readily andeffectively and results in the production of a finely divided productwhich is an extremely desirable material for mixing with solidnon-carbonaceous reducing agents to produce composite reagents for usein producing chromium-bearing metal products. Simple grinding to producea product in which ninety per cent of the particles are minus 100- meshresults in' conversion of more than fty per cent of the product toan\impalpable powder, a powder in which more than fifty per cent of thematerial (by weight) consists of particles small enough to pass a200-mesh screen. The extremely finely divided particles readily coat andtenaciously adhere to particles of solid non-v carbonaceous reducingagent with which they may be mixed and thus provide the intimate contactrequired for reduction to a very high degree with controlled oxidation.

In practicing my invention, advantage may be taken of the effect ofroasting in facilitating regrinding by subjecting the ferrochromium to apreliminary roasting operation in a relatively coarse state of divisionto accomplish fractional oxidation and subsequently re-grinding andreroasting one or more times, if necessary, to accomplish the desireddegree of oxidation. For example, the ferrochromium may be ground in thefirst instance to form a product, the major portion of which consists ofparticles not sub-` stantially smaller than required to pass through a(i5-mesh or equivalent screen (Tyler series). After roasting of thisrelatively coarse product to accomplish eiiicient oxidation in view ofits relatively coarse nature,l the roasted product may 4be subjected toa grinding operation to form a product, the major portion of whichconsists of particles small enough to pass a 1D0-mesh screen. 'I'heresulting more finely divided material may be roasted to effect afurther degree of oxidation.

Preliminary roasting (followed by re-grinding and re-roastlng) may becarried out with ferrochromium ground intially to any desired pa'rticlesize. Double or multiple roasting (preliminary roasting followed byre-grinding and reroasting) may be advantageous for several reasons. Forexample, the grinding of high carbon ferrochromium to produce a productof which a large proportion consists of particles small enough to pass a10o-mesh screen is a relatively simple matter, Therefore, the problem ofsecuring an ultimate oxidized product comprising particles of the mostdesirable small sizes can be simplified by combining the advantageswhich can be derived as a result oi the grinding characteristics of highcarbon ferrochromium with advantages which can be derived as a result ofthe grinding characteristics of the oxidized product.

Multiple roasting may be carried out with or without the presence ofoxidation promoters in any stage, or, when any stage of roasting iscarried out in the presence of one or more of such agents, additionalamounts may be added to the product of that stage of roasting beforesubjecting it to the next stage of roasting. Thus, for example, whenchromate formation is desired, I prefer to first roast finely dividedferrochromium at a relatively high temperature above 1000 C. in thepresence of suiiicient lime to form calcium chromite with all of thechromium in the ferrochromium and subsequently roast the productobtained by such roasting treatment at a temperature below 1000" C. inthe presence of auflicient additional lime and soda ash to provide atotal amount of calcium' oxide and sodium oxide to combine with all ofthe chromic oxide remaining unchanged to form chromate and chromite ofcalcium and sodium.

l Roasting operations may be facilitated by selection of theferrochromium to be treated. Highcarbon ferrochromium products grindmore readily and can be converted to desirably small particles moreeasily than low-carbon ferrochromium. Thus, -for example, ferrochromiumcontaining 8 to 10 per cent or more carbon can be reduced to the form ofa powder comprising very small particles quite easily; ferrochromiumcontaining 6 to 8 per cent carbon is more dinicultly reducible toparticles of desirablyA small sizes; and ferrochromium containing less'than about 6 per cent carbon can be reduced to particles desirablysmall in size only with considerable difficulty relatively to thedifficulties encountered in finely dividing ferrochromium productscontaining more than 6 per cent carbon.

The .grinding of relatively low-carbon ferrochromium is facilitated ifthe ferrochromium also contains silicon. Thus, for example,ferrochromium containing about 4 to 6 per cent carbon and amounts ofsilicon up to about 3 per cent can be ground quite readily.

In practicing my invention, I prefer to employ ferrochromium as nearlysaturated as possible with carbon, or, alternatively, ferrochromiumcontaining smaller amounts of carbon, but containing, also, sufiicientsilicon to compensate, in its influence upon grinding characteristics,for the carbon deficiency. When I produce the ferrochromium for roastingby reduction treatments of chromium-bearing materials, I prefer toemploy sufficient carbon to incorporate in the resulting ferrochromiumas much carbon as possible, and, if the conditions of operation are not-such as to permit the production of products of the higher carboncontent, I operate the `reduction process ,under conditions 'such as toreduce silicon from silica contained in the charge and form a productcontaining, preferably, about 1 to 3 per cent of silicon. Largerquantities of silicon improve the grinding characteristics of theferrochromium produced, but they are objectionable because they increasethe bulk of the slag producedin the ultimate reduction of the oxidizedproducts of the invention.

In forming the composite reagents of the invention, the roasted productand the solid` noncarbonaceous reducing agent maybe ground separatelyand mixed together subsequently or` the two products may' be groundtogether. I prefer to grind the two products together at least in thepreparation of the final composite reagent, as grinding of thetwoproducts together results in thorough mixing and aids in lcoating ofthe larger particles of each product with the extremely iine particlesof the other product, thus producing the most desirable type of intimatecontact. Grinding and mixing etliciencies are improved when the solidnon-carbonaceous reducing agent is ground preliminarily-,to a finelydivided condition. In employing silicon containing reducing agents,according to my preferred practice, Iemploy a 4reducing agent groundinitially to such an extent that a--large proportion consists ofparticles small enough to pass a 10o-mesh screen.

In the preferred composite reagents of my invention', the majority ofthe particles of the roasted material and non-carbonaceous reducingagent combined are small enough to pass a 1D0-mesh screen. Substantialamounts consist of particles small enough to pass a 150-mesh screen andof particles small enough to pass a 20D-mesh screen. Substantially allof the particles may be small enough to pass a 20G-mesh screen, and thistype of product is most desirable when the composite reagent is to beused for the direct production of a metal product containing iron andchromium in the proportions in which these elements are present in thecomponents of the composite reagent. When the composite reagent is to beemployed on the surface of a molten metalA bath for incorporatingchromium in the metal such a ne state of division of the components ofthe composite reagent is not so essential tothe securing of goodresults.

The products of my invention may be em- Y ployed in any suitable mannerfor producing chromium-bearing alloys. The oxidized products. forexample, may be added to the furnace either alone or in admixture withthe reducing agent when reduction is to be carried out in an electricfurnace where ample heat is available. When reduction is to be carriedout in combustion furnaces or in crucibles, the oxidized productpreferably is mixed intimately with the reducing agent before beingcharged into the furnace or crucible. The intimate mixture may beemployed in a loose condition, or it may be employed in a compactcondition, as. for example, in the form of briquettes, or tightly packedin combustible bags or metal containers. In adding the intimate mixtureof oxidized material and reducing agent to a combustion furnace, Iprefer to employ it in the form of a compact mass, as in the form ofbriquettes or agglomerates.

When the composite reagents are to be formed into briquettes or packedin containers, it is desirable to employ particles of different sizes inthe ranges 80 to 100 mesh; 100 to 150 mesh; 150 to 200 mesh; and minus200 mesh. Substantial amounts of the material will consist of particleswithin these size ranges when grinding is carried out under conditionsdesigned to accomplish subdivision of about to 10 per cent of thematerials to minus 200 mesh particles. The use of various sizedparticles provides for an effective degree of interlocking of particleswhich tends to produce strong briquettes capable of withstanding roughhandling in shipping and which also tends to aid in securing thedesirable intimate contact of particles of roasted material withparticles of reducing agent. The use of various sized particles alsoprovides for tight packing of the materials in containers.

In producing oxidized products from molten alloys of iron and chromium,oxidation may be carried out in any suitable manner. For example, amolten bath of the alloy may be blown with air or subjected to theaction of an oxide of iron. Oxidation preferably is carried out in thepresence of a base like calcium oxide to produce a workable slag. Whenlime is employed the chromium oxidized to chromic oxide enters intochemical combination with the calcium oxide of the lime, forming calciumchromite. Lime in the oxidized product is not objectionable, as itfunctions to flux the oxidized reducing agent in reducing operations towhich the oxidized product is subjected ultimately. Lime may be employedin any suitable amount, but, when the oxidized product is to be storedfor any considerable period of time, it preferably is used in arestricted or controlled amount such that the oxidized product willcontain no uncombined calcium oxide. Free or uncombined calcium oxideabsorbs moisture and carbon dioxide from the atmosphere which may causedangerous explosions (or carbon contamination of the metal after inconnection with the procedures for oxidizing alloys containing chromiumand iron at temperatures below their melting points.

When alloys containing iron and chromium are oxidized in the solidstate, any suitable temperatures below their melting points may beemployed. Preferably, the lowest temperatures capable of effecting thedesired degree of oxidation are employed.

I have discovered that oxidation of the iron, chromium and carbonproceeds rapidly and effectively when alloys containing these elementsare heated, in a fine state of division, to temperatures substantiallyhigher than 1200" C., but below the melting points of the alloys. Attemperatures below 1000 C., oxidation proceeds more slowly, and oxidizedproducts containing less than about 0.30 per cent of carbon (by weight)are diilcult to obtain. Even at temperatures as high as 1200" C.,products containing less than 0.20 per cent by weight of carbon arediilcult or impossible to produce with many hours of roasting underoxidizing conditions. At temperatures substantially higher than 1200 C.,products containing not more than about 0.10 per cent by weight ofcarbon and containing even as little as a trace of carbon can beproduced by roasting under oxidizing conditions for periods of timeshorter than two hours. In roasting to eilect a high degree of carbonelimination, I prefer to employ temperatures in excess of 1250 C. oreven in excess of 1300 C. Operating at temperatures above 1300 C., inthe range 1300u C. to 1350 C., with and without oxidation promoters, Ihave obtained oxidized products entirely free of carbon, products inwhich the presence of carbon could not be detected by the usualanalytical methods.

In carrying out roasting of ferrochromium in accordance with myinvention, I may produce oxidized products entirely free of carbon orproducts substantially free of carbon such, for example, as productscontaining not more than about 0.02 per cent or which contain less thanabout 0.05 per cent of carbon. I may produce, also, oxidized productscontaining carbon in amounts up to 0.10, 0.20, 0.30 per cent or more.

Materials consisting of particles larger than those which will pass a1D0-mesh screen can be roasted indefinitely at temperatures around 1000C. without total elimination of carbon being effected. Particle size isan important factor bearing on the matters of times and temperaturesrequired for oxidation and degrees of carbon elimination accomplished.In general, coarser products require longer periods of treatment and theuse of higher temperatures than finer products.

vless than one per cent of soda ash in the roast- Complete oxidation ofground ferrochromium by roasting at low temperatures-in one-operation isdiillcult to accomplish, kbut substantially complete oxidation may beobtained by roasting in the presence of lime and a little soda. l Inusing lime there are, in any event, several advantages. In subsequentreaction with silicon or ferro-silicon, lime is available for slaggingthe produced silica and accelerating its production. Ordinarily, inroasting in the presence of admixed lime, I prefer to use about equalamounts of lime and of ferrochromium. This may or may not be enough inrelation to the silica produced in subsequent reduction of the oxidizedmaterial with silicon-containing reducing agents. It, however, does givea, composition not subject to change in the air and thereforeadvantageous for shipping. More lime can be physically admixed beforethe exothermic action if it be wanted. Another advantage in roasting inthe presence of lime is that oxidation may be readily carried beyond theCraOa point with production of CrOs. In reaction with silicon, CrOaproduces considerably more heat than CraOz.

If desired, the roasting may convert substantially all the chromium tochromate. But it is usually better to .have in the roasted product aconsiderable percentage of CraOa. The reaction of CrOa with silicon is,as stated, more highly exothermic than that of CrzOa; that is, for equalquantities of chromium more heat is developed, the proportion of oxygenin CrOs being double that of CrzOa and theexcess being, so to speak,loosely bound. However, more slag is formed per unitl of chromium asCrOa, more silicon being oxidized to silica. The yield of chromium metalper unit of silicon used in reduction is greater from CrzOa than fromCrOs. It has been found advantageous in some cases to carry the roastingof ferrochromium so far as to give onlya minor proportion of thechromium as chromate. However, in other cases the proportion may behigher. Equal proportions of chromium in the two forms give a usefulproduct. Any desired content of oxygen within limits can be put into theproduct in roasting to chromate. When the oxidized material is to beused for adding molten chromium to small bodies of metal, as for examplein a foundry ladle, a higher oxygen content as CrO; in the materialgives more heat and a higher temperature to the molten chromiumaddition. Larger-operations, as in open hearth steel practice, requireless oxygen. Thus, in roasting ferrochromium, the oxygen content is madeto suit the particular purpose for which the product is to be utilized,the chromium content being inverse to the oxygen added in roasting.

In the roasting with lime the proportion of lchromate in the product canbe controlled by the roasting temperature, and also by the relativeamount of soda in the roasting mixture. temperature of roasting alsoaifects the elimination of carbon, as hereinbefore pointed out, highertemperatures being conducive to quicker elimination of carbon, and tosmaller chromate content, with higher chromite.

Roasting ferrochromium at temperatures well under 1000 C. with somewhatless than 100 per cent by weight of lime with no soda ash or with ingcharge converts the chromium mostly to chromate without completeoxidation and elimination of carbon from the ferrochrome metal in areasonable length of time. Above 1000" C. the

The`

carbon-is eliminated but the chromate breaks regulation of the tem"rature to control theratio of chromate to chromite (CrOa to CraOa) inthe oxidized product, and thus of the oxygen content and exothermicity.I have found, for example, that addition to a roasting mix offerrochromium and lime of soda ash (NazCOa) in the amount of about 2to'5 per cent by Weight of the ferrochromium metal results in about 50per cent conversion of the chromium to chromate in a short time withelimination of a substantial amount of carbon and oxidation of metalwhen the temperature of roasting is held around l000 C.; the remainingchromium being oxidized largely to chromic oxide (CrzOa). A small amountof the chromium will be present as metallic chromium which functions tobind the residual carbon. With more lime or more soda the proportions ofchromate is increased. A 50-50 oxidation of chromium to chromite andchromate gives an oxidized material' capable of a highly exothermicreaction with silicon alloys. Such a compound of CaO, FezOs, CrzOa andCrOz containing a small amount of NazO from the soda ash and made fromferrochromium by roasting in air, is a highly advantageous material forexothermic production of chromium-iron metal. A fully chromated materialcontaining CaO, NazO,

FezOs and CrOa in chemical combination can readily be made. It containsless chromium but is more exothermic.

It is however possible to oxidize highv carbonl ferrochromium completelyby roasting it in finely divided form without the presence of lime orother oxidation promoter; roasting being in two or more stages and thematerial being re-ground between the roasting stages. This shortens thetime and fuel required. Oxidation of ferrochromium containing 6 to 10per cent carbon is a vigorous exothermic action which starts at about600 to 700 C., the temperature rising automatically to 1000 C. orhigher. But substantially complete elimination of metal and of carbonrequires heating of the material for a time after the exothermic actionhas spent itself` and this time is materially shortened by the presenceof a base or other oxidation promoter with the ferrochromium. Doubleroasting has the advantage of facilitating grinding to a greateriineness than is usually possible for the unroasted metal. The lime andsoda are omitted with advantage in the first roasting and added insubsequent regrinding and re-roasting.

When roasting in two stages, the temperature may Well be carriedconsiderably above 1000D C. in the first. stage. 1350 C. for example, tosubstantially completely eliminate carbon and oxidize the Cr to CraOaand after re-grinding with lime and soda a second roasting at 700 to1000 C. puts a good percentage of CrOa in the product, a proportionwhich can be above per cent of the total contained chromium. It is oftenadvantageous in practice to roast to 100 per kcent CrO: and mix thefully chromated productwith chromite obtained by roasting at highertemperature for shorter time.

-sired for the subsequent exothermic action.

Oxidation can be accelerated by raisingV the partial pressure of oxygenin well understood ways. by the use of oxygen itself, or a compoundcapable of releasing oxygen at the roasting temperature, such as sodiumchlorate. sodium nitrate, sodium bichromate, chromium trioxide,manganese dioxide. or the like. The use of oxygen, by raising the owgencontent of the roasting atmosphere to a point above the ordinaryconcentration of oxygen in air, naturally facilitates oxidation. A smallquantity of one of the oxygen-releasing 'compounds mentioned, presentalong with the lime, also shortens the roasting time, such compoundserving when so used as an effective promoter of oxidation, whilerelying upon the air as the main source of oxygen.

The roasting step may in fact be conducted, with or without lime, in thepresence of a sumcient quantity of one of the oxidizing agents oroxygen-releasing compounds mentioned hereinabove to furnish owgen foroxidation of most or all of the metal. When this is done, the oxidationbecomes strongly exothermic and is completed in a few minutes.

However. in the ordinary practice of the present invention, air andlime, with a little soda, are relied on. Instead of lime, strontia orbaryta may be used but their molecular weights are higher and their costgreater. Potash may be used instead of soda. The bases may be used inthe fox-m of carbonates. Magnesia or dolomitic lime may be used.

'I'he roasting can be done in a roasting or calcining furnace ofsuitable type such as an open hearth or reverberatory furnace withmechanical rabbling or in a rotary kiln. stirring during roasting aidsoxidation. Fine grinding of the mixture in a pebble or ball mill beforeroasting is good practice.

'Ihe color of the roasted product is from black to gray to yellow.depending upon the CaO content and the CrO: content. Complete oxidationof ferrochromium is 'attended with loss of magnetism and the fullyroasted material is non-magnetic. In the roasting, oxidation of themetal and of the carbon proceed together, with loss of magnetic power asthe metal and carbon are eliminated with formation of FezO; and withoutformation of FeO. The magnetic test may be used to measure theelimination of metal, of- P'eO and of carbon, the roasting being stoppedwhen the material becomes non-magnetic.

If the synthetic chromite is insuiilciently high in CrtFe ratio, it maybe next beneilciated by replacement of iron with lime and preferentialreduction of iron. in the manner described in my Patent No. 2,098,176.Or the ore may be beneiiciated before reduction to high carbonferrochromium. Whether or not such beneiiciation is practiced. theresultant chromite, which may be calcium ferrichromite or a calciumchromite, or a chromated chromite, is then exothermically reducible witha non-carbonaceous reducing agent, such as ferrosilicon, ferrochromesilicon, aluminum, or the like. This reduction results in the productionof an iron-chromium alloy low in carbon; e. g. chromium steel", lowcarbon ferrochromium, or even (where iron has been selectively reducedand removed) a chromium metal of high purity. Low grade, high iron,materials are, however, advantageous in making chrome alloy steel andiron.

As a carbon-free reducing agent, any of the alloys of aluminum orsilicon. .or magnesium, may be used. Calcium, magnesium and aluminumsilicides are effective. Where nickel is wanted in the final alloy,nl'ckel silicide may form a component of the reducing agent. Ferrochromesilicon is useful in adding chromium with the heat developed inexothermic reduction of roasted ferrochrome by the silicon.

In accordance with one aspect of my invention, roasted ferrochromium ismixed with ferrosilicon or'ferrochrome silicon, both as fine powders, insuch quantity as to supply sufllcient silicon to reduce the chromium andiron oxides to metal. To make a good exothermic mixture reactingcompletely and quickly, it is necessary that the mixing be exceptionallycomplete. It is a useful expedient. after making the mixture to ballmill it for a time. The mixture is next introduced into a steel bath, asin the open hearth steel furnace, in such relative quantity as to supplythe desired chromium content in the final steel product. This step maybe the final step in standard open hearth steel manufacture; that is,the step when exothermic action is initiated and completed withproduction of molten metal which enters the steel, while the SiO:formed, as well as any BiO: present in the mixture added, combines withthe CaO present in the chromite to form a non-refractory slag; this slagbeing free-running at the steel-making temperature, and notobjectionable either in amount or in character. In making this additionto molten iron or steel. there is no local chilling. As a matter offact. with the usual exothermic mixtures, there is an increase intemperature. The exothermic mixture adds molten chromium to the steel.The mixture can be such as to add no silicon or a desired amount ofsilicon to the steel.

The advantage of tine particle size and intimate contact of theparticle, particularly in the manufacture of low carbon ferrochromewhere the allowable silicon content may be from 1 to 1.5 per cent, maybe illustrated by the following examples, of small Vscale tests.

A mix of roasted ferrochrome and ferrochrome silicon, 30.6 per centbeing plus 100 mesh, 65 per cent minus 100 mesh and plus 150 mesh, 4.1per cent minus 150 mesh and plus 200 mesh and 0.3 per cent minus 200mesh gave a metal, when the mix was ignited and the exothermic reactionallowed to proceed to completion, which contained 6.2 per cent Si. Thesame mix when ground to completely pass a 200 mesh screen gave a metalcontaining l per cent Si, which is within the specified range for Si inlow carbon ferrochrome.

Silicon control was not accomplished at the expense of chromiumrecovery. In fact the advantage of silicon control was supplemented byan advantage of additional or increased recovery of chromium. Therecovery in the second example above, employing the iiner material. wasapproximately seven per cent better than the recovery in the firstexample, employing the coarser material. Recoveries achieved in largescale operations usually exceed ninety per cent.

'Ihe control of silicon in the metal in one step is different from theprior art and is accomplished by the use of a roasted ferrochrome whichhas had the gangue of the ore removed and a product produced ofcontrolled oxygen content which allows the use of a high lime slag inthe exothermic reaction and still produces molten metal and molten slag.Such conditions are conducive to the silicon control in metal. Thissaves a refining operation to remove the silicon from the metal which isthe. general practice in common use.

The same eiliciency of silicon control in the metal can be accomplishedin the electric steel furnace or open hearthfurnacein making chromesteels if the same degree of fine grinding and contacting is practiced,with the advantage of a saving in time of making the heat and in powerused, as compared to the usual practice of using ferrochrome metal inmaking chromium steels. Coarser mixes can of course be used with varyingdegrees of economy particularly in 'furnaces like the electric furnacewhere additional heat is readily available to produce the hightemperatures needed. Under such conditions the time of reacting isprolonged.

In a modiiied embodiment of the invention, a chromium steel is producedentirely by exothermic reaction. In this method of operation, no steelbath is necessary, all of the iron needed for the subsequent steel overthat reduced from thev synthetic chromite being supplied through theferrosilicon or ferrochrome silicon used, the amount of chromium putinto the steel being correspondingly high. An oxygen-carrying compoundsuch as sodium nitrate, sodium chlorate, sodium bichromate, or the like,may be added with the roasted ferrochromium, and the amount of siliconadded in the reducing agent is made sumcient to supply silicon foroxidation by this `added material and to give suiicient heat in beingoxidized to melt the .whole of the mix,vin addition to that required forreducing the metal oxides of the chromite. Iron ore may be used in thesilicothermic mixture and steel of a desired composition made by theexothermic reaction-of iron oxide and ferrosilicon. As in the methodpreviously described, enough' lime should ordinarily be presentV in theexothermic mixture to form, with the resultant silica, as well as-anysilica present as such in the chromite. a slag having a lime-silicaratio of approximately 1.5:1 by weight. Where somewhat higher or lowerslag ratios are desirable in the steel-making operation, the lime andsilicon may be adjusted accordingly.

When it is not advisable to incorporate in the composite reagents orreaction mixtures sufficient lime to form, with the silica formed byoxidation of silicon employed for reduction and with any silica presentin the mixtures before reduction, a slag of the desirable compositori,the additional lime required may be acquired by the silica from a highlybasic slag with which the mixture may be placed in contact in thereduction receptacle. Thus, forlexample, in employing composite reagentsor reaction mixtures deficient in lime (calcium oxide), I prefer toplace them in contact with slag layers containing lime in excess of thatrequired to form a tri-calcio silicate with the silica present therein.Slag layers containing lime and silica in the ratio of four calciumoxide to one silica and higher have been employed satisfactorily. Thesilica produced extracts calcium oxide from the highly basic slagimmediately surrounding the zone of reaction.

The composite reagents in briquetted form function admirably when placedon slag layers overlying molten metal layers. They extend down throughthe slag layer and iioat on the surface of the metal layer. Reactiontakes place at the contact surfaces, and the brlquettes appear lorcomposite reagents preferably should not conto dissolve or melt awaysmoothly and uniformly, from the bottom up, with the solid upper portiondescending uniformly until entirely' submerged and consumed.

In forming the various reaction mixtures or 5 composite reagents forvarious uses, varying amounts of lime may be incorporated. Forsteelmaking, for example, lime sufllcient to provide a ratio of lime toAsilica inthe range of from 1: 1 to 1.5:1 may be provided, and forlow-carbon or carbon-free ferrochromium production, lime suiiicient toprovide a ratio of lime to silica in the range of from 1.5:1 to 2:1 maybe employed. As hereinbefore pointed out, the reaction mixtures 16 tainfree or uncombined lime. All lime present preferably should bechemically bound with compounds such as iron oxide, chromium oxide,silica and alumina present in the mixture. The mixture may containsuflicient lime to combine with all of such substances present, or thelime present may be insuflicient for this purpose. If the reactionmixture or composite reagent is to be formed and employedsubstantiallyimmediately, or within a short time after the oxidized material isproduced, any desired amount of lime in exeess of that required tobambine with the eempounds in the oxidized material may be employed. Inusing oxidized ferrochromium as described for making chrome steel intheopen hearth furnace an advantageous procedure is to mix it in powderedform with finely divided ferrochrome silicon to form a Silico-thermicmixture capable of converting itself by exothermic reaction into moltenchromium-iron metal and lime silicate slag; then igniting the mixture inan insulated furnace, allowing the reaction to complete itself andpouring the metal into the open hearth steel bath, with or without thesilicate slag. This procedure effects addition of molten low carbonferrochromium to the open-hearth refined steel. The amount of chromiumthus put into the steel is that required for the desired alloycomposition.

In utilizing oxidizedferrochromium as the oxidant and ferrosilicon asthe reducing agent in the exothermic mixture, all of the silicon can be.oxidized. With a small excess of silicon over this amount, some siliconwill enter the metal.

Following are examples showing specicl embodiments of my invention.

Example I A low grade chromite ore was reduced with carbon in asubmerged arc electric furnace to obtain ferrochromium metal containingsubstantially all the chromium and iron of the ore. This metal wasground with lime in a ball mill to a fineness of 100 mesh and roastedfor about one hour and a half at a maximum temperature of 1350 C. withstirring in a reverberatory furnace to obtain complete oxidation of .themetal and contained carbon. An artificial chromite, calciumferrichromite, was obtained. It contained only a trace of carbon. Thisroasted product was ground together with ferrosilicon toa neness of 100mesh and the mixture was fed in packages to a bath of molten steel in anelectric furnace. 'I'he mixture underwent a smooth exothermic reactiondeliver-ing molten metal in the form of globules and the feeding wasstopped when suilicient chromium was added to the steel. The alloyformed contained 18.7 per cent chromium and carbon under 0.1 per cent;this carbon coming partly from that in the steel and partly from theferrosilicon.

In the above example the low grade chrome ore analyzed:

= Per cent CnO; 13.85 Iron oxides (calculated as FeO) 12.00 MgO 21.18S105 35.70 A110; 2.02 CO; (ignition loss) 14.30

nl The ferrochromium obtained in melting this ore was 42 per centchromium, 48 per cent iron, 7 per cent carbon and 3 per cent silicon.Roasting this metal. ground and mixed with about equal weight oi' limelproduced'au artificial chromate of the following composition:

Per cent CnO; 26 FezO: 29 CaO 42 S: 2.7 Carbon Trace In utilising thislow carbon roasted product (containing per cent available oxygen) formaking .E 18 per cent chromium steel, 236 parts of the I.' weight) and2.2 per cent CrzOn. 'Ihe chromium recovery from the ferrochromium metalwas about 94 per cent.

Example II 0. To make chromium steel from roasted ferrochromium andferrosilicon alone, the 42:48 ferrochromium obtained from low gradechrome ore as in Example I was ground in a proportion of 100 parts with434 parts lime and roasted in a gas-fired rotary kiln at l300 C. to form563 parts of carbon-free calcium ferrichromate. This was ground lwith264 parts ferrosilicon (50 per cent Si) and mixed with 269 partspowdered sodium chlorate. The mixture was ignited in a refractorycontainer by a small thermite charge. A smooth and vigorous exothermicaction took place, the mixture converting itself into 218 parts ofmolten chrome-iron metal containing 17.4 per cent Cr and a lime silicateslag in which the CaO-SiOz ratio was around l.5:l. The slag containedless than l per cent CrzOa.

In this operation, the amount of ferrosilicon vwas suilicient to reduceall the iron and chromium of the roasted chromite and to react with theNaClOx of the mixture, forming NaCl which was volatilized in thereaction. 'Ihe silicon in the chrome steel product was less than 0.5 percent and the carbon less than 0.1 per cent.

Example III A high carbon ferrochromium made by total reduction of asubstandard chrome ore, and containing 61 per cent Cr, 8 per cent C, 3per cent Si and approximately 28 per cent Pie, was ground and mixed withlime and soda ash in a proportion of 132 parts lime and 5 parts soda per100 parts metal and the mixture was roasted on an open hearth for aboutan hour at a temperature of about 750 to 875 C. The roasted product wasa j chromated chromite, substantially carbon-free,

containing 28 per cent CrOa, 10 per cent CrzOa, 14 per cent FezOa, 44per. cent CaO, 1 per cent NazO and 2 per cent S102. AThis materialcontains 22 per cent chromium, about 10 per cent iron and 20 per centavailable oxygen as CrOa. CrnO: and FezOg. The roasting converted some69 per cent of the chromium to chromate and 31 per cent to' chromite.When this oxidized material is ground and mixed with 35 per cent byweight of 50 per cent ferrosilicon and the mixture ignited, it convertsitself into a low-carbon metal,

44 per cent Cr and 55 per cent Fe and a lime silicate slag; one hundredparts of oxidized ferrochromium and 35 parts ferrosilicon becoming about50 parts metal and 85 parts slag. In adequate quantity the mixtureproduces freerunning molten metal and slag.

'Ihe exothermic mixture' of Example IlI may be ignited by adding it to abath of molten iron or steel in relative quantity such as to dilute thechromium content to that wanted in the finished alloy. Or the mixturemay be reacted in a separate furnace and the molten metal product runinto the steel furnace. In a particular instance a chromated chromiteadmixed with ferrochromesilicon was added in steel drums to a 65 tonopen hearth steel heat after the carbon elimination. About 20 minutesafter addition of 6800 pounds of the chromite mixture, the steel wastapped with a chromium content of 1.2 per cent, representing a recoveryof 85 per cent of the chromium contained in the Silico-thermic mixture.Any desired quantity of such mixture may be added without raising thesilicon content of the steel.

I have also utilized a material composed of roasted ferrochromium andferrochrome silicon in intimate admixture for putting chromium into castiron in a 50 pound foundry ladle, at the same time diluting the'carbonand silicon contents of the cupola metal and also raising thetemperature of the metal somewhat, which facilitated the castingoperation. Increasing the strength of the cast iron by some 43 per centwas an important result. making is possible to vary the castings byladle additions. The diluting action of the hot ferro-metal added byexothermic action is a function of the iron oxide formed in roastingferrochromium as well as of the iron in the silicon alloy. For thisfunction, a roasted low grade ferrochromium high in iron is particularlyadapted, further dilution being effected.' if desired, by iron oxide andferrosilicon added to the exothermic mixture.

The reaction mixtures or composite reagents of the invention employingoxidation products produced through the use of soda ash as an oxygenpromoter may be formed into very strong briquettes merely by wetting thematerial with water in an amount equal to about 6 per cent of the weightof materials of the reaction mixture, forming the desired shapes, andbaking 'the shapes at temperatures in the range 200 C. to 600 C. todrive off the water. The sodium chromate formed by reaction of the sodaash with chromic anhydride produced during the oxidizing treatmentappears to form the elective bonding agent. Apparently, the sodiumchromate picks up water of crystallization which enters crystals aselimination of water proceeds in baking, which crystals forminterlocking structures briefly during baking and are dehydratedsubsequently. leaving, in eilect, a rigid sintered mass.

The oxidized products and the composite reagents'of the invention may beused in producing u.

alloys containingiron and steel ot any composition which can be producedthrough the use of such products and reagents.

Following are some of the various alloys which may be produced throughthe use of the products and reagents of the invention:

(1) High chromium steels:

18-8 type Maximum carbon 0.25. Minimum carbon 0.08. Ball-bearing type1.0% (II-17% Cr. Cutlery type .55.'?5% 0,-15-18 Cr.

2) cnromiummickemron '(austenmc) C si Mn ci Ni ou max.

0.25 1.25 0.75 8.60 0.20 0.50 4.00 10.00 0. 20 0. 50 0. 40 18. 00 0.252.50 0. 80 Z100 0. 20 0. 50 0. 60 20.00 0. 20 0. 50 0. 00 25. il) 0. 202.00 0. 60 25.00

(3) MISCELLANEOUS Elements in percentage of steel Type C Si Mn Cr Ni AlV 3% chromium .05-.25 .35 .40 4- 6 Turbine type .l2 .20 .40 l2-l3 .40Cutlery type .35 .20 .35 12-13 Cutlery modliled type .70 .40 .45 16-17Ball-bearing 1.05 .45 .40 16-17 P t alve t ter Ff?. .w 2.75 P t alve tiif2- l .c .90 l8% Cr iron l0 50 28% Criron.. .l5 .50 18-8 stainless.06. 20 50 This application is a continuation-in-part .of my priorcopending applications Serial No. 165,417, filed September 23, 1937 anda continuation-in-part of application Serial No. 221,003, filed July 23,1938. The production of chromate in accordance with my invention isdescribed and claimed in my co-pending application Serial No. 256,559,filed February 15, 1939.

In the accompanying drawing, I have shown for purposes of illustrationonly, and not for purposes of limitation, a flow sheet illustratingseveral of the possible chromium recovery processes which may be carriedout in employing the principles of the invention. Heavy lines have beenemployed to outline a complete chromium recovery process commencing withthe treatment of chrornite ore initially and indicating the productionultimately of desirable chromiumbearing metal products. By means ofbroken lines, I have illustrated alternative oxidizing operations, and,in light lines, I have indicated the use of various oxidizing agents,other than those produced directly in the oxidizing operations, informing reaction mixtures in accordance with the invention. The basicmaterial and oxidation promoter employed in the oxidation operations maybe added at any or all of the points indicated by the heavy solid lines.

What I claim is:

l. rihe method of producing a composite reagent suitable for use in theproduction of chromium alloys which comprises oxidizing carbonbearingferrochromium and forming an oxidized product low in carbon andcontaining iron and chromium in oxidized forms, and mixing the oxidizedproduct in the solid state with a solid non- '-'arbonaceous reducingagent capable of reducing the oxidized forms of iron and chromium i'nthe oxidized product to metallic iron and metallic chromium.

2. The method of producing a composite reagent suitable i'or use in theproduction of chromium alloys which comprises oxidizingcarbonbearingferrochromium in a solid. finely divided condition and forming anoxidized product low in carbon and containing iron and chromium inoxidized forms, and mixing the oxidized product with a solid, finelydivided, non-carbonaceous reducing agent capable of reducing theoxidized forms ot iron and chromium in the oxidized product to metalliciron and metallic chromium.

3. The method of producing a composite reagent suitable ior use in theproduction of chromium alloys which comprises oxidizing carbonbearingferrochromium in a solid, iinely divided condition and forming anoxidized product low in carbon and containing ferric oxide and chromicoxide, and mixing the oxidized product with a. solid, finely dividedsilicon-containing reducing agent and oxidizing material capable ofdeveloping by reaction with silicon a temperature higher than thoseresulting from reaction of ferric oxide and chromic oxide with silicon.

4. The method of producing a composite reagent suitable for use in theproduction of chromium alloys which comprises oxidizing carbonbearingferrochromium in a solid, iinely divided condition and forming anoxidized product low in carbon and containing ferric oxide and chromicoxide, and forming a mixture containing (1) the ferrie oxide and chromicoxide of the oxidized product, (2) solid, ilnely divided ferro-siliconand-(3) oxidizing material capable of developing by reaction withsilicon a temperature higher than those resulting from reaction offerrie oxide and chromic oxide with silicon.

5. 'I'he method of producing a composite reagent suitable for use in theproduction of chromium alloys which comprises oxidizing carbonbearingferrochromium in a solid, nely divided condition and in the presence oflime and forming an oxidized product low in carbon and containingcalcium oxide in chemical combination with chromium oxide, and mixingthe oxidized product with a solid, finely divided non-carbonaceousreducing agent capable of reducing the chromium oxide of the oxidizedproduct to metallic chromium.

6. The method of producing a composite reagent suitable for use in theproduction of chromium alloys which comprises oxidizing carbonbearingferrochromium in a solid, nely divided condition and in the presence oflime and forming an oxidized product low in carbon and containingcalcium oxide in chemical combination with chromium oxideand forming amixture containing the oxidized product and a solid, finely dividednon-carbonaceous reducing agent whose oxidation reaction product isamphoteric or acid and which is capable of reducing the chromium oxideof the oxidized product to metallic chromium.

7. 'Ihe method of producing a composite reagent suitable for use in theproduction of chromium alloys which comprises oxidizing carbonbearingferrochromium in a solid, nely divided condition and forming an oxidizedproduct low in carbon and containing oxidized chromium a substantialamount of which is in the form of chromium trioxide, and mixing theoxidized product with a solid, finely divided, non-carbonaceous reducingagent capable of reducing the oxidized chromium to metallic chromium.

13.-The method of producing a composite reagent suitable for use in theproduction of chromium alloys which comprises oxidizing carbonbearingferrochromium in a solid, finely divided condition and in the presenceof lime and forming an oxidized product low in carbon and containingcalcium oxide in chemical combination with oxidized chromium asubstantial amount of which is in the form of chromium trioxide, andmixing the oxidized product with a solid, ilnely divided,non-carbonaceous reducing agent capable of reducing the oxidizedchromium to metallic chromium.

9` 'I'he method of producing a composite reagent suitable for use in theproduction of chromium alloys which comprisessubjecting carbonbearingferrochromium in separate operations to oxidizing treatments at elevatedtemperatures in the presence of lime to form (1) a product low in carbonand containing oxidized chromium largely in the form of calcium chromiteand (2) a product low in carbon and containing oxidized chromium largelyin the form oi calcium chromate, and mixing the chromite and chromateproducts in the solid state with a solid, non-carbonaceous reducingagent capable of reducing the chromite and chromate to metallicchromium.

10. The method of producing a composite reagent suitable for use in theproduction of chromium alloys which comprises subjecting carbonbearingferrochromium to an oxidizing treatment and forming an oxidized productlow in carbon and in which chromium is present largely in the form ofchromic oxide, subjecting the oxidized product to a low-temperatureoxidizing treatment in the presence of calcium oxide and soda ash toform a product containing chromate, and mixing the chromate-bearingproduct with a solid, finely divided, non-carbonaceous reducing agentcapable of reducing to the metallic state the chromium contained in thechromate-bearing product.

11. A composite reagent suitable for use in the production of chromiumalloys which comprises (l) oxidized ferrochromium in solid, iinelydivided condition produced by oxidizing carbonbearing ferrochromium andforming a product low in carbon and containing iron and chromium inoxidized forms and (2) a solid, non-carbonaceous reducing agent capableof reducing the oxidized forms of iron and chromium to metallic iron andmetallic chromium.

12. A composite reagent suitable for use in the production of chromiumValloys which comprises (l) oxidized ferrochromium in solid, finelydivided condition produced by oxidizing carbonbearing ferrochromium insolid, finely divided condition and forming a product low in carbon andcontaining iron and chromium in oxidized forms and (2) a solid,non-carbonaceous redu'cing agent capable oi' reducing the oxidized formsof iron and chromium to metallic iron and metallic chromium.

13. A composite reagent suitable for use in the production of chromiumalloys which comprises (l) oxidized ferrochromium in solid, finelydivided condition produced by oxidizing carbonbearing ferrochromium insolid, finely divided condition and forming a product low in carbon andcontaining ferrie oxide and chromic oxide, (2) a solid, nnely dividedsilicon-containing reducing agent and (3) oxidizing material capable ofdeveloping by reaction with silicon a temperaananas condition andforming a product low in carbon and containing ferrie oxide and chromicoxide,

(2) solid, finely divided ferrosilicon and (3) oxidizing materialcapable of developing by reaction with silicon a temperature higher thanthose resulting from reaction of ferric oxide and chromic oxide withsilicon.

15. A composite reagent suitable for use in the production of chromiumalloys which comprises (l) oxidized ferrochromium in solid, ilnelydivided iorm produced by oxidizing carbon-bearing ferrochromium insolid, iinely divided condition and in the presence of lime and forminga product low in carbon and containing calcium oxide in chemicalcombination with chromium oxide and (2) a solid, finely divided,non-carbonaceous reducing agent capable of reducing the chromium oxideto metallic chromium.

16. A composite reagent suitable for use in the production of chromiumalloys which comprises (1) oxidized ferrochromium in solid, finelydivided form produced by oxidizing carbon-bearing ferrochromium insolid, finely divided condition and in the presence of lime and forminga product low in carbon and containing calcium oxide in chemicalcombination with chromium oxide and (2) a solid, finely divided,non-carbonaceous reducing agent whose oxidation reaction product isamphoteric 0r acid and which is capable of reducing the chromium oxideto metallic chromium.

17. A composite reagent suitable .for use in the production of chromiumalloys which comprises (l) oxidized ferrochromium in solid, finelydivided form produced by oxidizing carbon-bearing ferrochromium andforming a product low in carbon and containing iron oxide, chromic oxideand a substantial amount of chromium trioxide and (2) a solid, finelydivided, non-carbonaceous reducing agent capable of reducing the oxidesof iron and chromium to metallic iron and metallic chromium.

18. A composite reagent suitable for use in the production of chromiumalloys which comprises (1) oxidized ferrochromium in solid, finelydivided form produced by oxidizing carbon-bearing ferrochromium insolid, finely divided condition and in the presence of lime and forminga product low in carbon and containing calcium oxide in chemicalcombination with chromium oxide in which a substantial amount of thechromium is present in the form of chromium trioxide and (2) a solid,non-carbonaceous reducing agent capable of reducing the chromium oxideto metallic chromium.

19. A composite reagent suitable for use in the production of chromiumalloys comprising (l) a product containing oxidized chromium in whichthe chromium is present largely as calcium chromate, (2) a. productcontaining oxidized chromium in which the chromium is present largely ascalcium chromite, said products containing calcium chromate and calciumchromite being products resulting from oxidation treatments ofcarbon-bearing ferrochromium, and (3) a solid, noncarbonaceous reducingagent capable oi reducing the chromite and chromate to metallicchromium.

20. A composite reagent suitable for use in the production of chromiumalloys, formed by grinding a non-carbonaceous reducing agent in thepresence of oxidized ferrochromium produced by oxidizing carbon-bearingferrochromium at a in and being substantially free of uncombined.,

calcium oxide, the non-carbonaceous reducing agent being capable ofreducing the iron oxide and the chromium oxide to metallic iron andmetallic chromium and being present in an amount about suiiicient toreduce all of the chromium and iron present.

21. A composite reagent suitable for use in the production of chromiumalloys, formed by grinding a non-carbonaceous reducing agent in thepresence of oxidized ferrochromium produced by oxidizing carbon-bearingferrochromium at a temperature below its melting point and forming aproduct containing iron oxide and containing calcium oxide in chemicalcombination with chromium oxide, said productcontaining an amount ofcalcium oxide sufclent t0 combine with all of the chromium oxidecontained therein and being substantially free of uncombined calciumoxide, the non-carbonaceous red-ucing agent being capable of reducingthe iron oxide and the chromium oxide to metallic iron and metallicchromium and being present in an amount about sufficient to reduce allof the chromium and iron present, and the major portion of saidcomposite reagent consisting of particles small enough to pass a10D-mesh screen.

22. A composite reagent suitable for use in the production of metallicchromium by exothermic reaction, which comprises calcium chromite andcalcium chromate intimately mixed with a solid, nely divided,non-carbonaceous reducing agent capable of reducing to 4the metallicstate the chromium of the calcium chromite and calcium chromate.

23. A composite reagent suitable for use in the production of metallicchromium by exothermic reaction, which comprises calcium chromite,calcium chromate and sodium chromate intimately mixed with a solid,nnely divided, non-carbonaceous reducing agent capable of reducing tothe metallic state the chromium of the chromite and chromate compounds.

24. A composite reagent suitable for use in the production of metallicchromium by exothermic reaction, which comprises calcium chromite andcalcium chromate intimately mixed with a solid, nely dividedsilicon-containing reducing agent.

25. A composite reagent suitable for use in the production of metallicchromium by exothermic reaction, which comprises calcium chromite andcalcium chromate intimately mixed with a finely divided, solid,non-carbonaceous reducing agent, the amount of chromium present in themixture in the form of chromate being not substantially greater than theamount of chromium present in the mixture in the form of chromite.

26. A composite reagent suitable for use in the production of metallicchromium by exothermic reaction, which comprises calcium chromite andcalcium chromate intimately mixed with a ilnely divided, solid,silicon-containing reducing agent, the amount of chromium present in themixture in the form of chromate being not substantially greater than theamount of chromium present in the mixture in the form of chromite.

27. A composite reagent suitable for use in the production of metallicchromium by exothermic reaction, whichcomprises calcium chromite.calcium chromate, and sodium chromate intimately mixed with a finelydivided, solid, non-carbonaceous reducing agent, the amount of chromiumpresent in the mixture in the form of chromate being not substantiallygreater than the amount of chromium present in the mixture in the formof chromite.

28. A composite reagent suitable for use in the production of a metallicchromium-bearing product by exothermic reaction which consistsessentially oi' calcium oxide, ferric oxide, sodium oxide, chromic oxideand chromium trioxide intimately mixed with a silicon-containingreducing agent, the amount of chromium present in the mixture in theform of chromium trioxide being not substantially greater than theamount of chromium present in the mixture in the i'orm of chromic oxide:

29. A composite reagent suitable for use in the production of metallicchromium by exothermic reaction, which comprises calcium chromite andcalcium `chromate intimately mixed with a nely dividedsilicon-containing, reducing agent, the amount of chromium present inthe mixture in the form of. chromate being not substantially greaterthan the amount of chromium present in the mixture in the form ofchromite and the silicon and the oxygen available for reaction with thesilicon being present in such amount and proportion that the mixture iscapable upon ig-- nition of converting itself by exothermic reactioninto molten chromium-bearing metal and molten calcium silicate slag.

30. A composite reagent suitable for use in the production of metallicchromium by exothermic reaction, which comprises calcium chromite,calcium chromate and sodium chromate intimately mixed with a finelydivided silicon-containing reducing agent, the amount of chromiumpresent in the mixture in the form of chromate being not substantiallygreater than the amount of chromium present in the mixture in the formof chromite and the silicon and the oxygen available for reaction withthe silicon being present in such amount and proportion that the mixtureis capable upon ignition of converting itself by exothermic reactioninto molten chromium-bearing metal and molten calcium silicate slag.

3l. A product suitable for use in the production of metallicl chromiumcomprising calcium chromite and calcium chromate and containing anamount of chromium in the form of chromate not substantially in excessof the amount present in the form of chromite.

32; A product suitable for use in the production of metallic chromiumcomprising calcium chromite, sodium chromate and calcium chromate andcontaining an amount of chromium in the form of chromate notsubstantially in excess of the amount present in the form of chromite.

33. A product suitable for use in the production of a metallicchromium-bearing product, consisting essentially of calcium oxide,ferric oxide. sodium oxide, chromic oxide and chromium trioxide andcontaining an amc-unt of chromium in the form of chromium trioxide notsubstantially in excess of the amount present in the for of chromicoxide.

34. The method of producing a metallic alloy containing iron andchromium which comprises igniting a compositereagent comprising (l) aproduct 1o the 'solid omo produced by oxidizing carbon-bearingferro-chromium and forming an oxidized product low in carbon andcontaining iron and chromium in oxidized forms and (2) a solid,non-carbonaceous reducing agent capable of reducing the oxidized formsof iron and chromium in the oxidized product to metallic iron andmetallic chromium. l

35. The method of producing a metallic alloy containing iron andchromium which comprises igniting a composite reagent comprising (1) aproduct in the solid state produced by oxidizing carbon-bearingferro-chromium and forming an oxidized product low in carbon andcontaining calcium oxide and iron and chromium in oxidized forms and (2)a solid, finely divided, silicon-containing reducing agent.

36. The method of producing a metallic alloy containing iron andchromium which comprises igniting in contact with molten metal acomposite reagent comprising (l) a product in the solid state producedby oxidizing carbon-bearing ferrochromium and forming an oxidizedproduct low in carbon and containing iron and chromium in oxidized formsand (2) a solid, non-carbonaceous reducing agent capable of reducing theoxidized forms of iron and chromium in the oxidized product to metalliciron and metallic chromium.

37. The method of producing a metallic alloy containing iron andchromium which comprises igniting in contact with molten metal acomposite reagent comprising (l) a product in the solid state producedby oxidizing carbon-bearing ierrochromium and forming an oxidizedproduct low in carbon and containing calcium oxide and iron and chromiumin oxidized forms and (2) a solid, ilnely divided, silicon-containingreducing agent.

38. In a process of producing a low-carbo chrorniferous metal, the stepswhich comprise oxidizing a high-carbon ferrochromiumalloy to get rid ofcarbon and convert the metal content thereof to oxide form, therebyproducing a ferrous chromite product, selectively reducing iron oxidetherefrom in thev presence of lime to form a product containing calciumchromite, and reducing the calcium chromite product with anon-carbonaceous reducing agent.

39. Areaction mixture comprising (l) asilicon- -containing reducingagent, (2) oxidized ferrochromium produced by oxidizing carbon-bearingferrochromium in solid, iinely divided condition and forming a productlow in carbon and containing iron and chromium inoxidized forms and (3)lime in an amount such u to provide about 1.5 to 2.0 molecules ofcalcium oxide for each atom of silicon in the mixture.

40. The method oi' producing an alloy containing iron and chromium whichcomprises smelting chromium-bearing ore with carbon to producehigh-carbon ferrochromium, oxidizing the highcarbon ferrochromium andforming an oxidized product low in carbon and containing iron andchromium in oxidized forms, and reducing to the metallic state the ironand chromium of the oxides oi' iron and chromium contained in theoxidized product with a non-carbonaceous reducing agent to produce ametallic alloy containing iron and chromium.

41. The method of producing an alloy containing iron and chromium whichcomprises smelting chromium-bearing ore with carbon to producehigh-carbon ferrochromiurn, oxidizing the high-carbon ferrochromium andforming an oxidized product low in carbon and containing iron andchromium in oxidized forms, and reducing to the metallic state the ironand chromium oi the oxides of iron and chromium contained in theoxidized product with a silicon-containing reducing agent to produce ametallic' alloy containing iron and chromium.

42. The method of producing an alloy containing iron and chromiuml whichcomprises smelting chromium-bearing ore with carbon to producehigh-carbon ferrochromium, oxidizing the highcarbon ferrochromium andforming an oxidized product low in carbon and containing iron andchromium-in oxidized forms, and reducing to `the metallic state the ironand chromium of the oxides oi.' iron and chromium vcontained in theoxidized products with an aluminum-containing reducing agent to producea metallic alloy containing iron and chromium.

43. 'I'he method of producing an alloy containing iron and chromiumwhich comprises smelting chromite ore to eiect selective reduction ofiron contained therein with the production of a metal product high iniron and low in chromium and a benetlciated ore product high in chromiumand low in iron, smelting the beneciated ore product with carbon toproduce high-carbon terrochromium, oxidizing the high-carbon ferro'-chromium and forming an oxidized product low in carbon and containingoxides oi' iron and chromium, and reducing to the metallic state theiron and chromium of the oxides of iron and chromium contained in theoxidized product with a non-carbonaceous reducing agent to produce ametallic alloy containing iron and chromium.

44. The method of producing an alloy containing iron and chromium whichcomprises smelting chromite ore to eiIect selective reduction of ironcontained therein with the production of a metal product high in ironand low in chromium and a benenciated ore product high in chromium andlow in iron, smelting the beneflciated ore product with carbon toproduce high-carbon ferrochromium, oxidizing the high-carbonferrochromium and forming an oxidized product low in carbon andcontaining oxides oi iron and chromium, and reducing to the metallicstate the iron and chromium oi' the oxides of iron and chromiumcontained inthe oxidized product with a silicon-containing reducingagent to produce a metallic alloy containing iron and chromium.

45. 'Ihe method o! producing an alloy containing iron and chromium whichcomprises smelting chromite ore to efi'ect selective reduction of ironcontained therein with the production of a metal product high in ironand low in chromium and a benetlciated ore product high in chromium andlow in iron, smelting the beneilciated ore product with carbon toproduce Vhigh-carbon ferrochromium, oxidizing the high-carbonferrochromium and forming an oxidized product low in carbon andcontaining oxides of iron and chromium, and reducing to the metallicstate the iron and chromium of the oxides of iron and chromium containedin the oxidized product with an'aluminum-containing reducing agent toproduce a metallic alloy containing iron and chromium.

MARVIN J. UDY.

